The present invention is directed to the printing of nonwoven webs and the webs printed thereby. Specifically, the printed nonwoven webs are polyolefin fibrous webs printed with an ink exhibiting improved adhesion to the webs.
The printing of substrates, such as woven and nonwoven fabrics and films, is well known. The printing of fabrics with inks and dyes is a common and widely used method for imparting patterns and colors to a basic fabric. Many current personal care products, such as diapers and training pants, include printed designs to improve their appearance. A problem with such printed products is that the printed design can be smeared or even removed during the handling the products encounter during manufacturing and packaging.
Another problem with these earlier printed products is that when they are wetted, the printed ink can run, fade, smear, and the like.
Yet another problem is that the crawling action of babies and small children subjects the exterior portion of the diaper and training pant to a high degree of abrasion. Such abrasion will quickly remove any printing which is not durably adhered to the outer surface of the product. Many of these products employ polyolefins in the manufacture of the component materials.
Generally speaking, color printing on cellulosic substrates such as cotton is well known in the art. Printing on polar polymers such as nylon and polyester is possible, but difficult compared to the same type of printing on cellulosic materials. More difficult than either of these substrates is the printing of non-polar polymers such as polyolefins. This is particularly true of fibrous polyolefin structures such as nonwoven webs, because current inks and dyes have limited adhesion to these non-polar inert materials.
Ink print adhesion to nonwoven polyolefin fibrous webs can be somewhat improved through the use of corona discharge treatment on the webs. However, this requires an additional step in the printing process along with higher energy costs and/or lower line speeds. In addition, if the corona discharge treatment is not carefully monitored, there is the possibility that the treatment will burn the nonwoven web, thereby increasing production costs due to the waste of damaged material.
The choice of ink or dye can create further problems. Standard dyes used in the fabric industry generally cannot be absorbed by the nonwoven fibers. Commercial inks currently used by the printing industry have poor adhesion to nonwoven fibrous webs, such as nonwoven polyolefin fibrous webs. Ink resin bases which have affinity to nonwoven fibrous webs, such as nonwoven polyolefin fibrous webs, generally do not have good printing characteristics that achieve high quality graphic reproduction, and require active solvents that attack the printing media. For example, high acetate content ink can have adverse effects on photopolymer printing plates and rubber printing plates used for flexographic printing. These adverse effects include plate swelling and premature plate failure.
In summary, problems with prior art printing include poor adhesion, poor printing characteristics, poor mechanical rub resistance, and poor chemical resistance of inks on dyes used to print nonwoven fibrous webs.